ZABBIX is an enterprise-class distributed monitoring solution designed to monitor and track performance and availability of network servers, devices, and other IT resources. It supports distributed and Web-based monitoring, auto-discovery, real-time monitoring, SLA assurance, trending, and more.

Wireshark is a network protocol analyzer, or "packet sniffer", that lets you capture and interactively browse the contents of network frames. It provides a commercial-quality packet analyzer for Unix, and the most useful packet analyzer on any platform.

OpenNMS is the first enterprise-grade network
management platform developed using the open
source model. The three main functional areas of
OpenNMS are service polling, which monitors
services on the network and reports on their
"service level"; data collection from the remote
systems via SNMP in order to measure the
performance of the network; and a system for event
management and notifications.

GoAccess is a real-time Web log analyzer and interactive viewer for almost every Web server. It runs in a terminal and provides fast and valuable HTTP statistics for system administrators that require log monitoring and visual reports on the fly. GoAccess can monitor unique visitors, browsers, spiders, OS, hosts and IP geolocation, keyphrases, referring sites, status codes, etc. It has support for IPv6 and it parses nearly any Web log format.

LEAF is a secure, feature-rich, customizable embedded Linux network appliance for use in a variety of network topologies. Although it can be used in other ways, it's primarily used as a Internet gateway, router, firewall, and wireless access point.

Webminstats is a Webmin module designed to store system information in an rrdtool database and to display historic (hourly, daily, weekly, monthly, and custom) graphs. It is modular in design, so as to be able to log everything from CPU usage to email box size.

Check_MK is a complex addon for Nagios/Icinga and consists of three subprojects. The check and inventory system Check_MK is a general purpose Nagios plugin for retrieving data. It adopts a new approach for collecting data and obsoletes NRPE, check_by_ssh, NSClient, and check_snmp. It features a significant reduction of CPU use on the Nagios host and automatic inventory of items to be checked, and is especially useful with larger Nagios installations. "MK Livestatus" gives immediate and fast access to live and historic Nagios status data. It's a supported backend for many addons including NagVis, NagiosBP, and Thruk. "Check_MK Multisite" is a feature complete replacement for the Nagios GUI, and uses MK Livestatus as a backend. It is very fast, and supports efficient distributed monitoring.